The invention relates to a process for recovery of hydrocarbons from a fluid feed.
It is known to fractionate fluid feed streams containing hydrocarbons having at least two carbon atoms per molecule (C.sub.2) in addition to components having at most one carbon atom per molecule which components (e.g. hydrogen, methane, carbon oxides and/or nitrogen) have a lower boiling point than the C.sub.2 hydrocarbons, by means of one or more processes such as chilling, cryogenic separation, absorption and compression. However, the energy requirements of such processes are relatively high and whereas valuable components such as hydrogen generally remain in the low boiling (fuel) gas stream thus separated from the C.sub.2 hydrocarbons.
It is furthermore known to separate a particular component such as hydrogen or carbon dioxide selectively from a gaseous feed mixture containing other components (e.g. methane and other hydrocarbons or nitrogen) by contacting said feed mixture with one side of a membrane and removing the component which selectively permeates through the membrane from the other side thereof, before subjecting the non-permeated feed fraction to a cryogenic separation treatment.
A major disadvantage of such processes is, however, that substantial volumes of components having a relatively low boiling point are passed through a (e.g. cryogenic) fractionation unit which accordingly has to have a relatively high capacity for a given quantity of the initial feed mixture which is contacted with the membrane.
It is an object of the present invention to provide an efficient process for the recovery of c.sub.2 hydrocarbons from a fluid feed also containing components having at most one carbon atom per molecule without incurring the aforementioned disadvantages.
It has now been found that by using a membrane which is substantially impermeable to C.sub.2 hydrocarbons in a first separation step, and fractionating the retentate fluid obtained therefrom in a second separation step, a high separation efficiency can be attained with substantial savings in fractionation equipment, compared with a fractionation such as such.